Jemalloc-support: Added --with-jemalloc configure option

Selecting jemalloc, prevents static linking of rocksdb, as it
is dependent on tcmalloc. Default option remains tcmalloc.
Package build builds with tcmalloc support. Support for 
jemalloc in package build and perf stats/heap profiler is 
underway.

Signed-off-by: shishir gowda <shishir.gowda@sandisk.com>
it might make more sense to error out if tcmalloc and jemalloc are both enabled?